This invention relates to surface functionalization of pigments and/or dyes for radiation curable ink printing and coating applications.
In general, printing inks and coating materials can be classified in four categories: solvent-based, water-based, radiation-curable and powder materials. The compatibility between pigments/dyes and organic resins (as coating matrix or printing vehicles) is one of the most crucial factors affecting not only processability but also performance in both coating and ink printing industries. Pigments/dyes that are used in non-polar environments must be readily dispersible, and therefore hydrophobic. In contrast, pigments that are used in polar environments must exhibit highly polar surface characteristics. In the extreme cases of water-borne inks or coatings, the degree of polarity may need to be fully hydrophilic.
It is important to be able to render desired surface characteristics that can match the polarity of resins and diluents (solvents or water). Pigment/dye surface modification has been a challenge for a long time.
It is well known, for example, to use surfactants to improve the dispersibility of pigments, but the utility of such a process is usually limited. Short shelf life or relatively poor thermal stability of the pigment/dye dispersion is a main concern. An invention described in U.S. Pat. No. 5,808,118 relates to a surfactant consisting of the product of the simultaneous reaction of a sulfonic acid, a saturated fatty acid and a polyamine. The advantage of this invention is to provide better dispersion stability.
Organic silanes and silicone oligomers have been extensively employed as coupling agents in surface modification for various inorganic pigments such as transition metal oxides (U.S. Pat. Nos. 6,120,596, 5,665,155, 4,404,318, 5,719,206, 5,820,977, EP 0725115 WO 00/04421, WO 99/57204, etc.). Various hydrophobic groups were attached on the pigment surface through covalent bonds. The major limitation of this method is that no coupling reaction will take place between the organic silanes and the surface of pigments/dyes if there are no hydroxyl groups on the surface of the pigments/dyes.
A method for making a non-polar suspension of charged pigment particles is illustrated in WO 00/05313. In this method, a covalent bond is formed between the pigment and the surface modifying polymers which have one of the following groups: carboxyl, hydroxyl, anhydrido, amino, amido, halo, thiol, epoxy, keto, aldehydo, isocyanato, and alkenyl. Pigments can also be treated with nitrogen-containing copolymer of a variety of polyurethanes (U.S. Pat. No. 4,844,742).
Hydrophilic characteristics of pigment surface are provided in various ways. Organic pigments and transition metal containing pigments (hydrophobic) can be treated in phosphoric acid and/or its monoester (U.S. Pat. Nos. 5,865,885, 5,466,482 EP 0717085). Magnetic pigments can be surface treated in one or more aralkylphosphonic acids (U.S. Pat. No. 6,099,895). Pigments can be surface coated by mixing titanium oligomers and organic acid esters (EP 568720).
The mechanisms of chemical and physical adsorption are often used for pigment/dye surface treatments, although these types of links are not as stable as covalent bonds. Zinc oxide powder can be immersed in one or more organic liquids selected from alcohols, ketones, amines and esters (U.S. Pat. No. 5,672,427). Pigments can also be treated with poly (vinyl alkyl ether)s (EP 0500494)
In the U.S. Pat. No. 4,622,073, metal powder pigment is treated with an organic titanate having the general formula: Ti(OR)2[OC2H4N(C2H4OH)2]2 wherein R is alkyl group of 1 to 8 carbon atoms. In the U.S. Pat. No. 4,080,353, pigment is treated with titanate-phosphite adducts which are the reaction products of (RO)4Ti and di-substituted hydrogen phosphite (R′O)2P(O)H where R and R′ are monovalent alkyl, alkenyl, aryl, aralkyl or alkaryl.
Radiation (UV/electron beam) curable printing inks and coatings have become very well accepted technologies because their distinct advantages including low or non VOC, fast process, high performance, etc. However, formulating ink and coating materials is a challenge because of the poor compatibility between UV-resins and pigments/dyes, and therefore, poor dispersibility and wetting ability. None of above cited literature/patents has disclosed any method addressing this issue.